1. Field of the Invention
The present invention relates to a bending apparatus or machine employed to bend an elongated workpiece passing through stable and movable dies, one after the other, which movable die is allowed to move or shift relative to the stable die so as to bend the elongated workpiece.
The term “curve” may optionally include a line comprising nodes and arcs connecting the adjacent nodes in the following description.
2. Description of the Prior Art
A software program such as a numerical control (NC) program can be employed to control the operation of any types of machine tools, including a bending machine. The software program must specify control data such as data defining a displacement or shift amount of a movable die in the bending machine, for example. Heretofore, skilled operators or workers are in general forced to write down the control data based on their intuition and experience. The written control data is actually used to manufacture trial products for evaluation. The evaluation may induce update of the control data based on intuition and experience of skilled operators or workers. The update of the written control data may be repeated many times until the product as expected can be obtained with the bending machine.
For example, Japanese Patent Application Laid-open Nos. 9-327727 and 10-166064 disclose proposals to generate control data without reliance on intuition and experience of skilled operators or workers. The proposals may contribute to manufacture of a first trial product roughly reflecting the shape of the final product as expected. The operators are released from generation of an original control data fully dependent upon their intuition and experience. The proposals may serve to reduce the operators' burden on troublesome operations, such as repeated manufacture of trial products and repeated update of control data.
The proposals of the above-mentioned Laid-open Nos. 9-327727 and 10-166064 are designed to employ a single three-dimensional coordinate system in calculating the periodical positions or motional path of the movable die. The coordinate system is designed to define the x-axis corresponding to the direction of advancement for an elongated workpiece, in other words, the longitudinal axis of the elongated workpiece. The motional path of the movable die is thus regulated within a plane perpendicular to the x-axis in the three-dimensional coordinate system. However, it is the fact that a straight line cannot completely reflect the longitudinal axis of a bent elongated workpiece. The plane for the motional path of the movable die, perpendicular to the x-axis, tends to suffer from an inclined attitude within a three-dimensional machine coordinate system established in the actual bending machine. The definition for the positions of the movable die according to the aforementioned plane of the three-dimensional coordinate system consequently cannot contribute to manufacture of a product of the dimensional accuracy within a permissible range required for a practical use.
In general, a simple calculation for deriving the positions of the movable die, based on a shape data specifying an image of a designed product within a coordinate system, cannot eliminate dimensional deviations or errors in a manufactured product. Corrections or compensations should be included in data for the positions of the movable die for cancellation of dimensional deviations in a manufactured product. Such data suffers from variation depending upon factors, such as the magnitude of curvature in bending, the quality of the elongated workpiece, the sectional shape of the elongated workpiece, and so on. These factors inevitably induce difficulty to specify the quantity of the corrections or compensations. For example, all the corrections or compensations are specified based on actual measurements in the aforementioned Laid-open Nos. 9-327727 and 10-166064. One has to measure the corrections or compensations for every magnitude of the curvature. Moreover, such measurement should be effected for every quality as well as every sectional shape and size of the elongated workpiece. Operators should suffer from a troublesome collection of measurement results.
When a software program is to be specified for the control of a bending machine, a displacement or shift amount of the movable die in control data must relate with the feed speed of an elongated workpiece such as an extruded aluminum workpiece, for example. However, the feed speed of the straight elongated workpiece cannot easily be specified based on an image of a bent product in the three-dimensional coordinate system. The aforementioned Laid-open Nos. 9-327727 and 10-166064 completely fail to refer to a method of accurately specifying the feed speed of an elongated workpiece based on a shape data specifying the shape of the bent product.
For example, the shapes or designs for industrial products, such as automobiles and electric household appliances, cannot be determined without considering methods of manufacture or mass production. If torsion can be effected on an elongated workpiece in combination with bending in a bending machine, an increased variety can be realized in the shapes or designs for industrial products. Heretofore, no one proposes a bending machine capable of effecting torsion on an elongated workpiece as expected.